FA-63829 / Actuarial life tables / Member archive

Median and quantile future lifetime: Target is the fraction dead instead of surviving · case 04

Non-median quantiles are reversed.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input l (from age x) and p (per mille surviving, 0<p<1000 else 'invalid'; also l_0<=0). Find the first t with l_t <= l_0 p/1000 and interpolate linearly: t-1 + (l_{t-1}-target)/(l_{t-1}-l_t). No crossing -> 'beyond table'. Rounded to 6.

Why this case matters

Life-table arithmetic compounds across ages, so one misplaced index or assumption shifts every downstream value.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
upper quartile survival	`10.718304`	`10.154911`	Failed

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